Tantalum sintered body and capacitor using the sintered body

ABSTRACT

A tantalum sintered body comprising a pore size distribution having a plurality of peaks wherein out of a plurality of peaks, two peaks having a largest relative intensity and a second largest relative intensity have a pore diameter of 0.2 to 0.7 μm and a pore diameter of 0.7 to 3 μm, having a volume of pore 10 mm 3  or more including the volume of pore voids and a specific area of 0.2 to 7 m 2 /g, and having a CV value of 40,000 to 200,000 μFV/g when sintered at 1,300° C., and a capacitor using the sintered body.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is an application filed under U.S.C. § 111(a)claiming pursuant to 35 U.S.C. § 119(e) of the filing date of U.S.provisional application Serial No. 60/326,736 on Oct. 4, 2001 pursuantto 35 U.S.C. § 111(b).

TECHNICAL FIELD

[0002] The present invention relates to a tantalum capacitor having alarge capacitance appearance ratio and a tantalum sintered body for thecapacitor.

BACKGROUND ART

[0003] Tantalum is a chemically stable metal and therefore used forvarious uses. For example, tantalum is widely used as a capacitormaterial for electronic instruments such as cellular phone and personalcomputer. The tantalum used as a capacitor material is usually in thepowder shape and the powder particles are molded and then integrated bysintering to provide an electrode called a sintered body. The inside ofthe sintered body has a three-dimensional complicated form where thepowder particles are electrically/mechanically connected. In the insideand outside of this sintered body, a dielectric film layer is formed andthen a material working out to a counter electrode is impregnated,thereby fabricating a capacitor. Microscopically, the capacitance of themanufactured capacitor greatly depends on the contact state between thecounter electrode material and the dielectric film layer insofar as thedielectric film layer is uniformly attached to the surface inside andoutside the sintered body.

DISCLOSURE OF INVENTION

[0004] Assuming that the capacitance appearance ratio is 100% when anaqueous phosphoric acid solution is used as the counter electrodematerial and the contact state with the dielectric film layer isperfect, it has been difficult to achieve a capacitance appearance ratioof 100% by using an electrode material having a high viscosity,particularly, a solid electrode material. In particular, when thetantalum powder for capacitors has a small average particle size or whenthe sintered body obtained from the tantalum powder has a large shape,the difficulty increases and in an extreme case, the capacitanceappearance does not reach even 50%. If the capacitance appearance ratiois low as such, the capacitor manufactured also suffers frominsufficient moisture resistance in some cases.

[0005] As a result of extensive investigations to solve theabove-described problems, the present inventors have found that when thesintered body used has a pore diameter distribution having a pluralityof peaks, a high capacitance appearance ratio can be achieved and thecapacitor manufactured using the powder can have a high moistureresistance value. The present invention has been accomplished based onthis finding.

[0006] That is, the present invention relates to the following tantalumsintered body and a capacitor using the same.

[0007] (1) A tantalum sintered body comprising a pore size distributionhaving a plurality of peaks.

[0008] (2) The tantalum sintered body as described in 1 above, whereinout of a plurality of peaks, two peaks having a largest relativeintensity and a second largest relative intensity have a pore diameterof 0.2 to 0.7 μm and a pore diameter of 0.7 to 3 μm.

[0009] (3) The tantalum sintered body as described in 1 above, whereinout of a plurality of peaks, the peak having a largest relativeintensity has a pore diameter of 0.7 to 3 μm.

[0010] (4) The tantalum sintered body as described in any one of 1 to 3above, wherein the sintered body has a volume of 10 mm³ or moreincluding the volume of pore voids.

[0011] (5) The tantalum sintered body as described in any one of 1 to 4above, wherein the sintered body has a specific area of 0.2 to 7 m²/g.

[0012] (6) The tantalum sintered body as described in any one of 1 to 5above, wherein a part of the sintered body is nitrided.

[0013] (7) The tantalum sintered body as described in any one of 1 to 6above, wherein the sintered body is obtained from a tantalum powdercompact of giving a sintered body having a CV value of 40,000 to 200,000μFV/g when sintered at 1,300° C.

[0014] (8) A capacitor comprising the sintered body described in any oneof 1 to 7 above as an electrode, a dielectric material formed on thesurface of the sintered body, and a counter electrode provided on thedielectric material.

[0015] (9) The capacitor as described in 8 above, wherein the dielectricmaterial comprises a tantalum oxide as a main component.

[0016] (10) The capacitor as described in 9 above, wherein the tantalumoxide is formed by electrolytic oxidation.

[0017] (11) The capacitor as described in any one of 8 to 10 above,wherein the counter electrode is an electrically conducting polymerobtained by doping a dopant into a polymer containing a repeating unitrepresented by the following formula (1) or (2):

[0018] wherein R¹ to R⁴ each independently represents a monovalent groupselected from the group consisting of a hydrogen atom, a linear orbranched, saturated or unsaturated alkyl, alkoxy or alkylester grouphaving from 1 to 10 carbon atoms, a halogen atom, a nitro group, a cyanogroup, a primary, secondary or tertiary amino group, a CF₃ group, aphenyl group and a substituted phenyl group; the hydrocarbon chains ofR¹ and R², or R³ and R⁴ may combine with each other at an arbitraryposition to form a divalent chain for forming at least one 3-, 4-, 5-,6- or 7-membered saturated or unsaturated hydrocarbon cyclic structuretogether with the carbon atoms substituted by R¹ and R² or by R³ and R⁴;the cyclic combined chain may contain a bond of carbonyl, ether, ester,amide, sulfide, sulfinyl, sulfonyl or imino at an arbitrary position; Xrepresents an oxygen atom, a sulfur atom or a nitrogen atom; and R⁵ ispresent only when X is a nitrogen atom, and independently represents ahydrogen atom or a linear or branched, saturated or unsaturated alkylgroup having from 1 to 10 carbon atoms.

[0019] (12) The capacitor as described in 11 above, wherein the polymeris at least one selected from the group consisting of polypyrrole,polythiophene and substitution derivatives thereof.

[0020] (13) The capacitor as described in 12 above, wherein the polymeris an electrically conducting polymer containing a repeating unitrepresented by the following formula (3):

[0021] wherein R⁶ and R⁷ each independently represents a hydrogen atom,a linear or branched, saturated or unsaturated alkyl group having from 1to 6 carbon atoms, or a substituent for forming at least one 5-, 6- or7-membered saturated hydrocarbon cyclic structure containing two oxygenelements when the alkyl groups are combined with each other at anarbitrary position; and the cyclic structure includes a structure havinga vinylene bond which may be substituted, and a phenylene structurewhich may be substituted.

[0022] (14) The capacitor as described in 13 above, wherein theelectrically conducting polymer is an electrically conducting polymerobtained by doping a dopant into poly(3,4-ethylenedioxythiophene).

DETAILED DESCRIPTION OF INVENTION

[0023] One practical embodiment for obtaining the sintered body of thepresent invention and a capacitor using the sintered body is describedbelow.

[0024] The tantalum powder used as a starting material in the presentinvention can provide a sintered body usable as an electrode forcapacitors and includes not only tantalum but also compositionscomprising tantalum as a main component. Representative examples of suchcompositions include an alloy comprising tantalum as a main component.The main component means a component present in a proportion of morethan 50%. The powder comprising tantalum as a main component can beproduced from a generally available tantalum compound. For example, thetantalum powder can be obtained by the reduction of tantalum halide withmagnesium or sodium, the reduction of potassium fluorotantalate withsodium, the molten salt (NaCl+KCl) electrolysis of potassiumfluorotantalate on a nickel cathode, the reduction of tantalum pentoxidewith alkali metal, alkaline earth metal, carbon or hydrogen, or thegrinding/dehalogenation after the introduction of hydrogen into atantalum ingot.

[0025] The obtained tantalum powder may be further processed. Examplesof the processing method include a method of allowing the powder tostand in a vacuum at a high temperature of 500 to 2,000° C. and thenwet- or dry-cracking the powder, a method of mixing the powder with anappropriate binder such as acrylic resin or polyvinyl alcohol and thencracking the powder, and a method of mixing the powder with anappropriate compound such as acrylic resin or camphor, allowing it tostand in a vacuum at a high temperature, and then wet- or dry-crackingthe powder.

[0026] The final powder usually has a particle size of, in terms of anaverage particle size, from 10 to 300 μm. The average particle size canbe freely adjusted, for example, by the classification after grinding orby the mixing of an appropriate amount of non-ground powder aftergrinding.

[0027] The tantalum powder may be partially nitrided. In order toproduce a sintered body from the powder and form a dielectric materialon the surface of the sintered body as described later to have a smallLC value, the nitrided amount is preferably from 10 to 100,000 mass ppm,more preferably from 300 to 7,000 mass ppm. The nitrided amount as usedherein is not nitrogen adsorbed to the powder but means a ratio of theamount of nitrogen reacted with tantalum to form a nitride, in thesintered body.

[0028] The nitridation of powder may be performed for the tantalumpowder in any step described above and the nitridation may be performedby any one of liquid nitridation, ion nitridation and gas nitridation orby a combination thereof.

[0029] A gas nitridation treatment by a nitrogen gas atmosphere ispreferred, because the apparatus is simple and the operation is easy.For example, the gas nitridation by a nitrogen gas atmosphere isachieved by allowing the powder to stand in a nitrogen atmosphere. Witha nitridation atmosphere temperature of 2,000° C. or less and a standingtime of several hours, a powder having an objective nitrided amount canbe obtained. By performing the treatment at a high temperature, thetreatment time can be shortened. The nitrided amount of the powder canbe controlled by the conditions of nitridation temperature andnitridation time of the material Lo be nitrided, which are confirmed bya preliminary test or the like.

[0030] The sintered body of the present invention is produced bysintering the above-described powder. One example of the method forproducing the sintered body is described below, however, the productionmethod of the sintered body is not limited to this example.

[0031] The sintered body can be obtained, for example, by press-moldingthe powder into a predetermined shape and heating it at 500 to 2,000° C.under a pressure of 10⁻¹ to 10⁻⁴ Pa for a few minutes to a few hours.The pressure at the press molding is set higher than the pressurecapable of molding the powder and lower than the pressure of giving asintered body having one pore diameter distribution peak. This pressurerange varies depending on the conditions such as properties of powderand press-molding machine used, however, can be decided by a preliminarytest.

[0032] When the compact obtained by such a method is sintered, forexample, at 1,300° C., the sintered body has a CV value (a product of achemical forming voltage and a 120 Hz capacitance when chemically formedat 80° C. for 120 minutes in an aqueous 0.1 mass % phosphoric acidsolution) of 40,000 to 200,000 μFV/g.

[0033] The thus-obtained sintered body of the present invention has apore diameter distribution having a plurality of peaks. Out of aplurality of peaks, two peaks having a largest relative intensity and asecond largest relative intensity have a pore diameter of 0.2 to 0.7 μmand a pore diameter of 0.7 to 3 μm, preferably a pore diameter of 0.2 to0.7 μm and a pore diameter of 0.9 to 3 μm. A capacitor produced fromthis sintered body can have good moisture resistance. Furthermore, outof these two peaks, the peak in the larger diameter side preferably hasa larger relative intensity, because the capacitor can have highermoisture resistance. The relative intensity is a differential value ofthe cumulative pore volume.

[0034] The thus-produced sintered body of the present invention has aspecific surface area of, for example, from 0.2 to 7 m²/g.

[0035] In general, as the shape of the sintered body is larger, theimpregnation of the counter electrode becomes more difficult. Therefore,the sintered body of the present invention can be preferably applied tocapacitors requiring a large sintered body and is particularly effectivewhen the sintered body required has a size of 10 mm³ or more.

[0036] The sintered body of the present invention may be partiallynitrided. The nitridation can be performed in the same manner as themethod described above as method for nitriding the powder. Thenitridation amount (concentration) of the sintered body is preferably atthe same level with the nitridation amount of the powder.

[0037] It is also possible to partially nitride a tantalum powder forthe production of a sintered body and further partially nitride thesintered body produced from the powder.

[0038] The sintered body of the present invention usually contains anatural oxidization oxygen contained in the tantalum powder and anoxygen added by the natural oxidation after sintering in an amount of500 to 70,000 mass ppm. In the sintered body of the present invention,the content of elements except for tantalum, oxygen, nitrogen and analloy-forming element with tantalum, is 400 mass ppm or less.

[0039] By preparing a lead wire having appropriate shape and lengthcomposed of a valve-acting metal such as niobium or tantalum at themanufacture of the sintered body of the present invention, the powdermay be press-molded such that a part of the lead wire is inserted insidethe compact and integrally molded to serve as an outgoing lead wire ofthe sintered body.

[0040] Using this sintered body for one part electrode, a capacitor canbe produced by interposing a dielectric material between this one partelectrode and the counter electrode. Examples of the dielectric materialfor the capacitor include dielectric materials comprising a tantalumoxide as a main component. For example, the dielectric materialcomprising a tantalum oxide as a main component can be obtained bychemically forming the tantalum sintered body as one part electrode inan electrolytic solution. For chemically forming the tantalum electrodein an electrolytic solution, an aqueous protonic acid solution isgenerally used, such as an aqueous 0.1% acetic acid solution or anaqueous sulfuric acid solution. In the case where a dielectric materialcomprising a tantalum oxide as a main component is obtained bychemically forming the tantalum electrode in an electrolytic solution,the capacitor of the present invention is an electrolytic capacitor andthe tantalum sintered body side serves as an anode.

[0041] On the other hand, the counter electrode of the capacitor of thepresent invention is, for example, at least one compound selected fromelectrolytic solutions, organic semiconductors and inorganicsemiconductors known in the art of aluminum electrolytic capacitor.

[0042] Specific examples of the electrolytic solution include adimethylformamide-ethylene glycol mixed solution having dissolvedtherein 5 mass % of isobutyltripropylammonium borotetrafluorideelectrolyte, and a propylene carbonate-ethylene glycol mixed solutionhaving dissolved therein 7 mass % of tetraethylammoniumborotetrafluoride.

[0043] Specific examples of the organic semiconductor include an organicsemiconductor comprising a benzopyrroline tetramer and chloranile, anorganic semiconductor mainly comprising tetrathiotetracene, an organicsemiconductor mainly comprising tetracyanoquinodimethane, and an organicsemiconductor mainly comprising an electrically conducting polymerobtained by doping a dopant into a polymer containing a repeating unitrepresented by the following formula (1) or (2):

[0044] wherein R¹ to R⁴ each independently represents a monovalent groupselected from the group consisting of a hydrogen atom, a linear orbranched, saturated or unsaturated alkyl, alkoxy or alkyl ester grouphaving from 1 to 10 carbon atoms, a halogen atom, a nitro group, a cyanogroup, a primary, secondary or tertiary amino group, a CF₃ group, aphenyl group and a substituted phenyl group; the hydrocarbon chains ofR¹ and R², or R³ and R⁴ may combine with each other at an arbitraryposition to form a divalent chain for forming at least one 3-, 4-, 5-,6- or 7-membered saturated or unsaturated hydrocarbon cyclic structuretogether with the carbon atoms substituted by R¹ and R² or by R³ and R⁴;the cyclic combined chain may contain a bond of carbonyl, ether, ester,amide, sulfide, sulfinyl, sulfonyl or imino at an arbitrary position; Xrepresents an oxygen atom, a sulfur atom or a nitrogen atom; and R⁵ ispresent only when X is a nitrogen atom, and independently represents ahydrogen atom or a linear or branched, saturated or unsaturated alkylgroup having from 1 to 10 carbon atoms.

[0045] In the present invention, the electrically conducting polymercontaining a repeating unit represented by formula (1) is preferably anelectrically conducting polymer containing a structure unit representedby the following formula (3) as a repeating unit:

[0046] wherein R⁶ and R⁷ each independently represents a hydrogen atom,a linear or branched, saturated or unsaturated alkyl group having from 1to 6 carbon atoms, or a substituent for forming at least one 5-, 6- or7-membered saturated hydrocarbon cyclic structure containing two oxygenelements when the alkyl groups are combined with each other at anarbitrary position; and the cyclic structure includes a structure havinga vinylene bond which may be substituted, and a phenylene structurewhich may be substituted.

[0047] The electrically conducting polymer containing such a chemicalstructure bears electrical charge and is doped with a dopant. For thedopant, known dopants can be used without limitation.

[0048] Examples of the polymer containing a repeating unit representedby formula (1), (2) or (3) Include polyaniline, polyoxyphenylene,polyphenylene sulfide, polythiophene, polyfuran, polypyrrole,polymethylpyrrole and substitution derivatives and copolymers thereof.Among these, preferred are polypyrrole, polythiophene and substitutionderivatives thereof (e.g., poly(3,4-ethylenedioxythiophene)).

[0049] Specific examples of the inorganic semiconductor include aninorganic semiconductor mainly comprising lead dioxide or manganesedioxide, and an inorganic semiconductor comprising tri-iron tetroxide.These semiconductors may be used individually or in combination of twoor more thereof.

[0050] When the organic or inorganic semiconductor used has anelectrical conductivity of 10⁻² to 10³ S/cm, the capacitor produced canhave a smaller impedance value and can be more increased in thecapacitance at a high frequency.

[0051] In the case where the counter electrode is solid, an electricallyconducting layer may be provided thereon so as to attain good electricalcontact with an exterior outgoing lead (for example, lead frame).

[0052] The electrically conducting layer can be formed using, forexample, solidification of an electrically conducting paste, plating,vapor deposition of metal or formation of a heat-resistant electricallyconducting resin film. Preferred examples of the electrically conductingpaste include silver paste, copper paste, aluminum paste, carbon pasteand nickel paste. These pastes may be used individually or incombination of two or more thereof. In the case of using two or morekinds of pastes, the pastes may be mixed or may be superposed one onanother as separate layers. The electrically conducting paste applied isthen solidified by allowing it to stand in air or under heating.Examples of the plating include nickel plating, copper plating, silverplating and aluminum plating. Examples of the metal vapor-depositedinclude aluminum, nickel, copper and silver.

[0053] More specifically, for example, a carbon paste and a silver pasteare stacked in this order on the counter electrode and these are moldedwith a material such as epoxy resin, whereby a capacitor is fabricated.This capacitor may have a niobium or tantalum lead which is integrallysintered and molded with the sintered body or welded afterward.

[0054] The thus-fabricated capacitor of the present invention isjacketed using, for example, resin mold, resin case, metallic jacketcase, dipping of resin or laminate film, and then used as a capacitorproduct for various uses.

[0055] When the counter electrode is a liquid, the capacitor fabricatedfrom two electrodes and a dielectric material is housed in a canelectrically connected to the counter electrode, thereby completing thecapacitor. In this case, the electrode side of the sintered body isguided outside through the tantalum or niobium lead and at the sametime, insulated from the can using an insulating rubber or the like.

BEST MODE FOR CARRYING OUT THE INVENTION

[0056] The present invention is described in greater detail below byreferring to Examples, however, the present invention is not limited tothe Examples.

[0057] The nitrogen and oxygen contents of the tantalum sintered body inthe following examples were determined using a nitrogen-oxygen analyzermanufactured by LECO Corporation.

[0058] The pore size distribution of the sintered body was measuredusing Autopore 9200 manufactured by Shimadzu Corporation.

[0059] The capacitance of the capacitor was measured by LCR metermanufactured by Hewlett Packard Company.

[0060] The CV value of the sintered body was determined from the productof a chemical forming voltage 20 V and a capacitance measured in 30%sulfuric acid after the chemical forming was performed in an aqueous0.1% acetic acid solution at 80° C. for 200 minutes while applying avoltage of 20 V.

[0061] The capacitance appearance ratio was expressed by a ratio of acapacitance in 30% sulfuric acid when the chemical forming was performedfor 1,000 minutes under the above-described conditions, which is takenas 100%, to a capacitance after the fabrication of a capacitor.

[0062] The moisture resistance value of the capacitor is expressed bythe number of units showing, when the capacitor was produced and leftstanding at 60° C. and 95% RH for 500 hours, a capacitance of less than110% or less than 120% of the initial value. As the number of unitsshowing a capacitance of less than 110% is larger, the moistureresistance was judged higher. The number of samples produced fordetermining the capacitance appearance ratio and the moisture resistancevalue was 30 units in each Example.

[0063] In the measurement of particle size, the particle sizedistribution was measured by a laser diffraction scattering method usingHRA 9320-X100 manufactured by Microtrac Inc. The particle size (D50; μm)when the cumulative vol % corresponded to 50 vol % was designated as theaverage particle size.

EXAMPLES 1 TO 6

[0064] A hydride of a tantalum ingot was ground and dehydrogenated toobtain primary particles having an average particle size of 0.7 μm. Anoperation of burning and then grinding the primary particles wasrepeated a plurality of times to obtain a granulated tantalum powder.Then, 0.15 g of the granulated powder was charged into a metal moldtogether with a separately prepared tantalum wire having a length of 10mm and a size of 0.30 mm and pressed by applying a load(N) shown inTable 1 using a molding machine to obtain a compact having a size of4.0×3.5×1.8 mm. Subsequently, the compacts each was sintered at 1,300°C. for 30 minutes to obtain a sintered body shown in Table 1.

[0065] The size, specific surface area and CV value of the sintered bodyof Example 1 were 23.7 mm3, 0.8 m²/g and 52,000 μLFV/g, respectively. Inthe other Examples, these values each was within +3% of Example 1.

EXAMPLES 7 TO 9

[0066] Sintered bodies were obtained in the same manner as in Examples 1to 3 except that the average particle size of the primary particles wasadjusted to 0.5 μm by classifying the primary particles in Examples 1 to3. The size, specific surface area and CV value of the sintered body ofExample 7 were 24.9 mm³, 1.1 m²/g and 69,000 μFV/g, respectively. Inother Examples and Comparative Examples, these values each was within±1% of Example 7.

COMPARATIVE EXAMPLES 1 TO 3

[0067] Sintered bodies were produced in the same manner as in Examples 1to 3 except that a tantalum powder obtained by reducing potassiumfluorotantalate with sodium and heat-treating the resulting tantalumpowder at 1,100° C. was used in place of the granulated tantalum powderused in Examples 1 to 3. The size, specific surface area and CV value ofthe sintered body of Comparative Example 1 were 24.3 mm³, 0.8 m²/g and53,000 μV/g, respectively. In other Comparative Examples, these valueseach was within ±2% of Comparative Example 1. The pore diameterdistribution of each sintered body produced is shown in Table 1. TABLE 1Pore Distribution Example and Pore Pore Peak Having Comparative MoldingDiameter of Diameter of Larger Relative Example Load, N Peak 1, μm Peak2, μm Intensity Example 1 392 0.67 1 2 Example 2 686 0.4 1.4 2 Example 3981 0.27 0.78 2 Example 4 490 0.35 2.2 2 Example 5 785 0.49 0.95 2Example 6 294 0.61 2.8 2 Example 7 392 0.52 2.2 2 Example 8 686 0.44 2.82 Example 9 981 0.35 1.2 1 Comparative 490 0.62 none — Example 1Comparative 686 0.55 none — Example 2 Comparative 392 0.82 none —Example 3

[0068] 60 Units of each sintered body produced in the same manner asthose of Examples 1 to 9 to 3 each was chemically formed at 80° C. for1,000 minutes while applying 20 V in an aqueous 0.1% phosphoric acidsolution to form an oxide dielectric film layer on the surface of thesintered body. The chemically formed sintered bodies were divided intogroups each consisting of 30 units and two kinds of cathode agents A andB shown in Table 2 were impregnated into 30 units of respective groups.Thereafter, a carbon paste and a silver paste were stacked in this orderand the device as a whole was molded with an epoxy resin to manufacturea chip-type capacitor. The capacitance appearance ratio and the moistureresistance value of each capacitor manufactured are shown in Table 3.TABLE 2 Method of Impregnating Method Cathode Agent Cathode Agent APolypyrrole A sintered body attached with ammonium persulfate andanthraquinonesulfonic acid was repeatedly subjected to vapor phasepolymerization with pyrrole vapor. B A mixture of lead A sintered bodywas repeatedly dioxide and lead dipped in a mixed solution of sulfate(lead lead acetate and ammonium dioxide: 98 mass %) persulfate.

[0069] TABLE 3 Moisture Resistance Value Number of Number of Method ofUnits Having Units Having Impregnating Capacitance CapacitanceCapacitance Cathode Appearance of of Agent Ratio, % 100-110% 110-120%Example 1 A 82 30/30  0/30 B 88 30/30  0/30 Example 2 A 85 30/30  0/30 B87 30/30  0/30 Example 3 A 79 27/30  3/30 Example 4 A 84 30/30  0/30Example 5 A 80 30/30  0/30 Example 6 A 82 30/30  0/30 Example 7 A 8530/30  0/30 Example 8 A 81 30/30  0/30 Example 9 A 82 30/30  0/30Comparative A 71 16/30 14/30 Example 1 Comparative A 69 11/30 19/30Example 2 Comparative A 73 17/30 13/30 Example 3

[0070] On comparison between Table 1 and Table 3, it is seen that thetantalum sintered body of the present invention has a plurality of peaksin the pore size distribution and therefore, a capacitor having a largecapacitance appearance ratio and good moisture resistance property canbe manufactured.

[0071] Industrial Applicability

[0072] When a tantalum sintered body of the present invention having aplurality of peaks in the pore size distribution, particularly atantalum sintered body where out of a plurality of peaks, two peakshaving a largest relative intensity and a second largest relativeintensity have a pore diameter of 0.2 to 0.7 μm and a pore diameter of0.7 to 3 μm, is used, a capacitor having a large capacitance appearanceratio and good humidity resistance property can be manufactured.

1. A tantalum sintered body comprising a pore size distribution having aplurality of peaks.
 2. The tantalum sintered body as claimed in claim 1,wherein out of a plurality of peaks, two peaks having a largest relativeintensity and a second largest relative intensity have a pore diameterof 0.2 to 0.7 μm and a pore diameter of 0.7 to 3 μm.
 3. The tantalumsintered body as claimed in claim 1, wherein out of a plurality ofpeaks, the peak having a largest relative intensity has a pore diameterof 0.7 to 3 μm.
 4. The tantalum sintered body as claimed in any one ofclaims 1 to 3, wherein the sintered body has a volume of 10 mm³or moreincluding the volume of pore voids.
 5. The tantalum sintered body asclaimed in any one of claims 1 to 4, wherein the sintered body has aspecific area of 0.2 to 7 m²/g.
 6. The tantalum sintered body as claimedin any one of claims 1 to 5, wherein a part of the sintered body isnitrided.
 7. The tantalum sintered body as claimed in any one of claims1 to 6, wherein the sintered body is obtained from a tantalum powdercompact of giving a sintered body having a CV value of 40,000 to 200,000μFV/g when sintered at 1,300° C.
 8. A capacitor comprising the sinteredbody described in any one of claims 1 to 7 as an electrode, a dielectricmaterial formed on the surface of the sintered body, and a counterelectrode provided on the dielectric material.
 9. The capacitor asclaimed in claim 8, wherein the dielectric material comprises a tantalumoxide as a main component.
 10. The capacitor as claimed in claim 9,wherein the tantalum oxide is formed by electrolytic oxidation.
 11. Thecapacitor as claimed in any one of claims 8 to 10, wherein the counterelectrode is an electrically conducting polymer obtained by doping adopant into a polymer containing a repeating unit represented by thefollowing formula (1) or (2):

wherein R¹ to R⁴ each independently represents a monovalent groupselected from the group consisting of a hydrogen atom, a linear orbranched, saturated or unsaturated alkyl, alkoxy or alkylester grouphaving from 1 to 10 carbon atoms, a halogen atom, a nitro group, a cyanogroup, a primary, secondary or tertiary amino group, a CF₃ group, aphenyl group and a substituted phenyl group; the hydrocarbon chains ofR¹ and R², or R³ and R⁴ may combine with each other at an arbitraryposition to form a divalent chain for forming at least one 3-, 4-, 5-,6- or 7-membered saturated or unsaturated hydrocarbon cyclic structuretogether with the carbon atoms substituted by R¹ and R² or by R³ and R⁴;the cyclic combined chain may contain a bond of carbonyl, ether, ester,amide, sulfide, sulfinyl, sulfonyl or imino at an arbitrary position; Xrepresents an oxygen atom, a sulfur atom or a nitrogen atom; and R⁵ ispresent only when X is a nitrogen atom, and independently represents ahydrogen atom or a linear or branched, saturated or unsaturated alkylgroup having from 1 to 10 carbon atoms.
 12. The capacitor as claimed inclaim 11, wherein the polymer is at least one selected from the groupconsisting of polypyrrole, polythiophene and substitution derivativesthereof.
 13. The capacitor as claimed in claim 12, wherein the polymeris an electrically conducting polymer containing a repeating unitrepresented by the following formula (3):

wherein R⁶ and R⁷ each independently represents a hydrogen atom, alinear or branched, saturated or unsaturated alkyl group having from 1to 6 carbon atoms, or a substituent for forming at least one 5-, 6- or7-membered saturated hydrocarbon cyclic structure containing two oxygenelements when the alkyl groups are combined with each other at anarbitrary position; and the cyclic -structure includes a structurehaving a vinylene bond which may be substituted, and a phenylenestructure which may be substituted.
 14. The capacitor as claimed inclaim 13, wherein the electrically conducting polymer is an electricallyconducting polymer obtained by doping a dopant intopoly(3,4-ethylenedioxythiophene).